What's the best way to make a long, hollow cylinder composed of filigree?
Its not pretty but ...

Here I used the Bezier curves to make a basic design, you might be better off using a vector package like Inkscape and then importing your design.
Note that it is Cyclic, 2D, Extruded and Beveled.


I then converted the Curve into a Mesh (not sure that step is strictly necessary) and then added an Array modifier.


Created a Bezier Circle and rotated it by 90 degrees on the X and scaled it by 4.


Then added a Curve modifier after the array and set it to the new Circle.


This all took minutes and is bit rough, but I hope it gives you some ideas.